The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Modern automatic motor vehicle transmissions utilize a several quart or liter fill of transmission fluid (hydraulic oil). The transmission fluid serves several purposes. First and most obvious is the lubrication of the numerous rotating and moving parts within the transmission. Second is the transfer of heat out of the transmission to maintain an appropriate operating temperature and third is use in the pressurized hydraulic control system of the transmission.
To achieve proper heat transfer to the ambient, a transmission oil cooler remote from the transmission is provided with a flow of transmission fluid. The oil cooler may be mounted within the vehicle radiator in which case heat is first transferred to engine coolant within the radiator and thence to the ambient or the oil cooler may be directly exposed to air flow, for example, through the engine compartment.
Such a device addresses only one aspect of transmission fluid temperature control however: ensuring that the transmission fluid temperature and thus the internal components of the transmission do not exceed design operating limits. While such a purpose is of great importance, there are other operating considerations relating to transmission fluid temperature. For example, when a vehicle and its transmission are started in cold weather, the viscosity of the cold transmission fluid can cause significant parasitic frictional losses. Depending upon the temperature, it can be several minutes before the transmission fluid temperature rises into a range where frictional losses become negligible. This delay is primarily due to the fact that only frictional heating from the rotation of parts heats the transmission fluid. During this time, fuel economy can be significantly degraded.
It is therefore apparent that improved control of automatic transmission fluid temperature is desirable.